Blending of polymers to make new compositions is well known. However finding polymer pairs that give useful mechanical properties is difficult. The unfavorable free energy of mixing for large polymeric molecules usually gives blends where the two polymers are separated from each other and have little or no affinity. These blends have poor mechanical properties and are not very useful for making molded articles or films. In some very limited instances two polymers show enough affinity to give sufficient adhesion between the two polymers that blends with good mechanical properties are obtained. In very rare instances the polymers have sufficient affinity to overcome the unfavorable thermodynamics of mixing and form an intimate mixture where the two polymers are dissolved in one another. Such miscible blends are very useful in that they are transparent, and often show good mechanical and rheological properties. Despite years of experimentation it is still very hard to predict, a priori, polymer miscibility.
We have found that a surprisingly small change in aryl polyester and aryl polyester carbonate structures allows one to go from blends that are phase separated and opaque to blends that are fully miscible and transparent. Incorporation of aryl ester linkages based on resorcinol, rather than bisphenol A (BPA), gives polyester carbonates that are miscible with polyimides, especially polyetherimides.
Even more surprising blends of three different polymers, resorcinol based polyester carbonates, polyimides and polyesters are also found to be miscible and transparent. Such miscible bends with polyimides are best achieved in compositions where the polyester carbonates or polyarylates contain at least about 50 mole % resorcinol based aryl ester linkages.